Concentration of iron ores by froth flotation



United States Patent CONCENTRATION OF [IRON ORES BY FROTH FLOTATIONBallard H. Clemmons, Tuscaloosa, Ala.

No Drawing. Application May 29, 1952, Serial No. 290,843

6 Claims. (Cl. 209-166) (Granted under Title 35, U. S. Code (1952), sec.266) The invention described herein may be manufactured and used by orfor the Government of the United States for governmental purposeswithout the payment to me of any royalty thereon in accordance with theprovisions of the act of April 30, 1928 (ch. 460, 45 Stat. L. 467).

This invention relates to the beneficiation of oxidized iron ores andmore particularly to the beneficiation of oxidized calcareous iron oresby froth flotation of calcareous diluents from an alkaline pulp of theore.

Conventional iron-ore beneficiation processes take little or nocognizance of the calcite contained in certain ores, but are concernedprimarily with rejection of the maximum amount of insoluble matterpossible.

This invention has as an object the development of an improved processfor the isolation of calcium-containing minerals from oxidized ironminerals.

A further object is the development of a flotation process for obtainingcalcium-containing concentrates of high purity from calcareous oxidizediron ores.

A still further object is the isolation by flotation of thecalcium-containing minerals present in certain iron ores, with a minimumloss of iron from the resulting concentrated iron product.

Another object is the isolation by flotation of the calcium-containingminerals from oxidized iron ores while retarding the flotation of theiron oxides and insoluble materials.

Other objects, purposes, and desirable features of the invention willappear hereinafter or will be understood from the subsequent descriptionof its practice.

The invention accordingly comprises a method of isolating the calcareousconstituents of various iron ores by employing anionic-collecting agentsto float the calcareous material from caustic alkaline iron ore pulpshaving a pH at least as high as about 9.3, while retarding flotation ofthe iron oxides with water-soluble silicates. Proper control of pulp pHis of considerable importance. Dextrin, soda ash, lignin sulfonate, ormixtures of these materials in moderation may be used as supplementaryreagents in conjunction with the various water-soluble silicates, ifdesired, but are not obligatory in the practice of this invention.

My experiments show that any of the soluble silicates (ortho-, meta-, orsesqui-silicates) can be used in the practice of this invention uponproper adjustment of reagent quantities. I prefer, however, to use theleast expensive form commonly known as water glass.

The soluble silicates are so well-known in industry that any discussionof their nature seems largely unnecessary. However, concisely, solublesilicates are manufactured by fusing finely divided silica (SiOz) and analkaline material such as soda ash. The fused product resembles glassbut may be dissolved, by special processes, in water. A number ofdifferent grades may be produced by varying the proportions of theingredients, or by special processes which produce specific properties,but the ratio of alkali to silica normally lies between 123.2 and1:3.86. The soluble silicates are very largely marketed as watersolutions or as readily soluble hydrated powders.

In the practice of this invention, desliming is neither necessary norespecially desirable, particularly when a maximum rejection ofcalcareous material is desired. Flotataion of deslimed charges may beaccomplished without difiiculty, but the reagent combination readilyenables filming and flotation of slime calcite as well as granularcalcite. Froths are compact, heavily mineral- 2,701,057 Patented Feb. 1,1955 ized, and clean readily to yield concentrates of high quality.

Although caustic alkaline pulps with a pH of approximately 10 arepreferred in the practice of this invention, acceptable results havebeen obtained throughout the range of about pH 9.3 to about 12.0. Ironslimes are most eifectively retarded at a pH value above 9.5, andconcurrently, anionic collector efficiencies are increased above this pHvalue. In practice, the indicated pH range of operation is ofconsiderable importance. Tests have been made in which visuallywell-dispersed pulps have been obtained at pH values ranging down to8.0. Nevertheless, optimum conditions for calcite flotation from ironores were not established below a pH of 9.3 and only partial flotationof calcite in relatively barren or lightly mineralized froths wasobtained. Moderate quantities of alkaline reagents other than caustic,such as other alkali metal hydroxides, ammonium hydroxide, sodiumsulfide, sodium carbonate, or mixtures of these materials, may be usedto augment the natural alkaline reaction of the silicates in pHadjustment. Reasonable quantities of hydrated lime may also be used asan alkalizer in the separation, although such a use in one sense defeatsthe purpose of isolating moderately pure calcite for subsequentcontrolled blending with the final iron products, as the lime activatesfine silica to anionic flotation so that a part of the mineral, ifpresent in the ore being treated, reports in the calcite concentrate.

A moderate amount of calcium and magnesium salts may be present in thewater used in the process without deleterious effect. Thus, soft wateris not a prerequisite of the separation.

The anion-active collecting agents suitable for the selective flotationof calcite from iron oxides and silica include the higher fatty acids,exemplified by red oil or oleic acid, purified or crude soaps of theseacids, fishoil soaps, fish-oil fatty acids, paper-mill sulfate soaps,and tall oils. Sulfonated petroleum products also may be used to replacepart of the red oil.

The quantities of the various reagents utilized in the practice of thisinvention are subject to considerable variation, and optimum quantitiesare best determined by experimentation for any particular ore or producttreated. Purity and yield of separated products are reliable guides forreagent adjustment. A large excess of collecting agent, under theconditions of trial, tends to float additional iron minerals in theroughing operation, but the latter are retarded without dilficulty insubsequent cleaners. A deficiency of collector results in incompleteflotation of the calcite. Large excesses of soluble silicate tend toretard calcite, whereas a deficiency results in little more than partialcollection of the calcite and decrease in selectivity as regards ironoxides. Frothing agents such as the higher alcohols, pine oil, cresylicacid, etc., may be used to advantage in the cleaning operations. Acritical study of the results of numerous batch flotation testsindicates that the relatively large optimum quantity of silicate used inbatch work may be considerably reduced in continuous operation, as itwill be readily apparent to those skilled in the art that the largequantities of calcite reporting in the middlings whenever silicateconcentrations are somewhat reduced in batch work in all probabilitywould in part report in the finished concentrates when middlings wereretreated by con ventional continuous operation flotation methods.However, the higher than normal pH must be maintained to obtaincontinued selectivity.

In describing the results of tests made on various iron ores, forsimplicity and convenience, the cleaner tailings or middlings from thetwo cleaning or refloating operations, being enriched in iron, will becalculated in a composite iron product composed of flotation tailingsand middlings (cleaner tailings). As stated above, it will be apparentthat the grade of the middlings and hence the Fe product would beimproved by recirculation in plant operations.

It will also be noted that the removal of calcite of necessity resultsin an increase in the insoluble matter content of the ores. In acopending application Serial No. 290,842, filed May 29, 1952, in which Iam a joint inventor there is described a two-stage process forselectively removing calcite and silica from oxidized iron ores asindividual concentrates.

The invention will be further illustrated, but is not intended to belimited by the following examples of tional sodium silicate to retardthe remaining iron oxides. The pine oil improved the froth condition ofthe second cleaner.

The final calcite rejects, the combined iron concentrates practice, 5(cleaner tailings) from the cleaning steps, and the rougher Example 1iron concentrates were drled, we1ghed, and assayed. A l p The results ofthe test were as follows: of relanvely 9 grade hlghly carequb Assay,percent Distribution, percent l1mon1t1c 1ron ore was obtained from anoperatmg mlne P d in the Longwy area of eastern France. The ore was Tonot 5: Fe (38,0 [H501 Fe 0 ,0 IHSOL typical of the area and was largelycomprised of oolitic limonite associated with calcite, an iron silicatemineral, Calcite product 3&3 44.1 L8 10.0 92,1 a small lim0illt4 ofquartz 0A heiad6 ;1nalys1s give F (lfim cgtratcsz 1 3 3 7 68 3 percente, percent a an percent y- 8 arm 47.6 drochloric acid insoluble(hereinafter referred to as Cleaner 2L9 insol.). Composite 03.7 46.4 2.29.4 90.0 7.9 90.2 In carrying out the flotation process according tothis QE 100-0 100-0 100-0 invention, the iron ore or product to betreated is first The calcite fraction isolated accounted for 36.3 perground to a suitable size for flotation (if not already of t 0f thWeight f the feed, Contained Percent such size) by standard orconventional methods. The 20 of the CaO present in the ore, and only10.0 percent of fineness of grind may vary from 35 to 200 mesh or finer,the Fe and 9.8 percent of the insol. The grade of the depending on thesize required for substantially complete iron product was raised from32.9 percent to 46.4 percent liberation of the ferruginous minerals fromthe diluents or Fe with a 90 percent recovery of the iron values. gangueminerals. Although overgrinding is to be avoided, These results wereabout average of those obtained on good liberation is essential for asatisfactory flotation charges of this calcareous limonite ore ground invarious separation. On the present ore, grinding to pass 100 mesh typesof mills to pass 65, 100, and 200 mesh, respectively. yielded acceptableresults. The calcite was rejected without dificulty in the tests by A250-gram portion of minus 20 mesh rolls crushed 1151115 Pounds P ton fthe Various anlofllc ore was ground with 400 cc. water to pass 100 meshin a q g g m helfltofore Inentjonfid, together With laboratory rod millcontaining 25 pounds of /z-inch steel ficlent alkallllflg agents toProvide 3 P from t0 rods. The ground charge was then transferred to asmall Example 2 mechanical flotationpeu of standard. i and suficcientThe eflect of variations in the quantity of soluble silitaRWateT addedto glve a Pulp contammg about 25 Percent cate retardant is shown in thefollowing example. Sevsohdseral individual 250-gram charges of thecalcareous limo- Flotat1on Of the calcareous constltuent Of the ore 13Snitic French re were ground to pass mesh in the then achleved m f P P ofmanner of Example 1. These charges, including slime, m ff Ted 011 i0161c acld) as conecfor were individually subjected to identicalflotation condi- Pf N Bfand sodlum F (a Commerclal 809mm tions (similarto those of Example 1, using 1.12 pounds lllcate havlflg a NaZO-SIOZTatlo of comaln' red oil per ton of ore) other than for variations inthe 8 appl'oxlmately 63 Percent Water; slllcate reagent 40 quantity ofsodium silicate used as iron and insol recharges Show" in these examplesare based on the Watel' tardant and small adjustments in the quantity ofcaustic, solution as received") as the silica and iron oxide detomaintain a constant pulp pH of 10.0. Results are pressant. The reagentcharge used expressed in the consummarized in the following table:

Froth product Iron product (middlings-i-tailing) Soluble Test silicateAssay, percent 090 Assay, percent Recovery, percent lb./t. ore Weight1'ec., Weight percent perpercent Fe CaO Insol. cent Fe 020 Insol. Fe0210 Insol.

ventional terms of pounds of reagent per ton of ore was It is readilyapparent from a study of the table that, as follows: although moderatelyhigh calcite rejections were obtained when quantities of silicate of 2pounds and above Conditioner Cleaner per ton of ore were used (provideda pulp pH above 9.3 Reagent Rougher was obtained), optimum results werenot obtained until No.1 No.2 No. 1 No.2 the concentration of reagentreached 8-12 pounds per ton of ore treated. Furthermore, frothcharacteristics sodium silicate, were progressively better as thisconcentration was in- Brand 120 1. creased. Higher quantities (test G)tended to retard R94 the calcite. Pine 0il 0.08 E l 3 T11ne,1n1n 2.5 2.52.5 1+2 1+2 P 6 Pulp P In the preceding examples of practice, solublesilicates alone were employed to retard the iron oxides during The pulp,including approximately 30 percent by weight anionic flotation of thecalcareous constituents of the ore. of slimed ore finer than 20 micronsin size, was condi- I shall now describe the results of flotation testswherein tioned for flotation in two stages. In the first conditionerauxiliary addition agents are employed to supplement the the sodiumsilicate established the desired alkalinity and 76 soluble silicates inthe practice of my invention. A numretarded the iron oxides andsiliceous material. In the her of variations, employing smallerconcentrations of second conditioner the ore was conditioned with thered silicate in conjunction with various supplementary disoil, asindicated. This filmed and prepared the calcareous persants, such aslignin sulfonates, dextrins, soda ash, etc., constituents for flotation.Air was then allowed to enter were tried. It was found that certain ofthese reagents the cell and resulted in the immediate formation of a 30could be utilized advantageously to reduce the quantity compact, heavilymineralized froth of the calcareous maof silicate required, thoughuniformly best results from terials. The froth was collected for 2.5minutes wherethe standpoint of froth characteristics were obtained whenupon flotation was complete. This rougher froth was the silicate wasused alone. In all instances, adjustment cleaned by refloating, asindicated, in the same cell using of pulp pH to at least 9.3 was a basicrequirement. By tap water for makeup, and using a small amount ofaddimeans of some of the reagent combinations, thoroughly dispersedpulps were obtained in the pH range of 8-9, but under the conditions oftrial, a satisfactory calctie rejection was not eifected.

Employing minus 100-mesh charges of the same ore, as well as the generaltest procedure used in Example 1, the following composited iron productswere obtained by use of auxiliary agents supplementing the iron oxideretarding effect of the soluble silicates. In all instances w 1 his t Fe'l' e g percen COIDPOSI e Condltmner calcite'product assay, per PercentPercent Test cent Fe re- OaO recovery jection Reagents pH RougherCleaner Fe 0410 N21200: 0.8 A SllicateN-- 0.5 9.15 15.5 0.0

Red Oil 1. 2s Silicate N 12.

11 5 5 7 5 52. 4 .0 46. 2.4 77.1 9 .0 Red Oil 1. 12 3 Silicate N-- 12.0E NaOH 4.0 10.9 49.5 35.9 44.1 4.2 87.5 84.1

Red 011 0. 32

NaOH, as needed, was used to adjust the pulp pH to Likewise, it will benoted that collector efficiency was about 10.0. low in test A and thatnone of the calcite carried through Pounds Percent Percent Deprcssantused per Assay percent Fe re- Q20 reton Fe Cao Insol covered ected NBrand Sodium Silicate 1. 0 43. 2 4. 0 8. 8 90. 8 84.1 Yellow CornDextrin. 1. 0 N Brand Sodium Silicate 1.0 44. 5 4. 2 8. 3 89. 7 84. 6Lignin Sullonate.... 1.0 N" Brand Sodium cate 1. 0 44. 7 3. 9 8. 6 89. 085. 7 Soda Ash 1.0 Composite, Feed (all tests) 32.6 17.6 6 3 100.0 100.0

It will be seen that the grade of the products produced in this fashioncompare favorably with those obtained in tests utilizing silicate aloneas retardant. Best froth characteristics, however, were obtained in thenormal high silicate tests.

Example 4 The importance of maintenance of a proper pulp pH in thepractice of my invention, as previously mentioned, cannot beoveremphasized. This factor is of prime importance not only with regardto optimum iron oxide retardation, but also with reference toessentially complete removal of calcite from the pulp. The combinationof reagents used in the practice of my invention with pulps within theproper pH range results in both good collector etficiency and highselectivity. There is no sacrifice of selectivity in order to obtainhigh collector efliciency, as might be expected by those versed in thisart. Anionic or soap flotation of minerals from pulps having a pH above9.5 results in considerably increased collector efficiency. Optimumselectivity with reference to the retardation of iron oxide minerals andflotation of calcite is achieved in accordance with the presentinvention in the pH range above 9.3-9.5. Below that point, in thoseinstances where flotation can be achieved by means of anionic collectingagents, both iron oxide and calcareous minerals tend to float in anon-selective manner. The foregoing observations are illustrated asfollows:

Several 250-gram charges of the limonitic ore of Example l Were groundthrough 100 mesh and floated (without being deslimed) in the mannerpreviously described. The feed contained 32.6 percent iron (largely aslimonite), 17.6 percent CaO, and 6.3 percent acid insoluble matter. Ineach test the rougher froth product was cleaned or refioated twice toyield a cleaner reject or final calcite product. Similarly, in eachtest, the two cleaner tailings or middlings were combined by calculationwith the rougher tailing or machine discharge to yield a composite ironconcentrate. In continuous operation, of course, the middlings would berecirculated and it may be anticipated that the over-all grade offinished product would be slightly better than is indicated in thepresent batch work.

the cleaning operation. In the higher pH range, filming efliciencyincreased progressively (tests B, C, D) until it was possible in test Eto reduce the collector to a third the quantity previously used.Relatively little change in the character or grade of the finishedproduct was noted, although in the extremely high pH range (test D) apart of the ferruginous minerals again showed a tendency to film andfloat. However, this factor is considered of secondary importance asoperation probably would best be undertaken in the 9.5 to 11.0 pH rangefrom both an economic and equipment corrosion standpoint.

Example 5 The flotation tests heretofore reported were all made on atypical calcareous hydrated iron oxide or limonite ore. I shall nowconsider the application of my method of flotation to a typicalcalcareous iron ore in which the iron values are present in the form ofan earthy type of hematite. In the particular ore to be considered atthis time, there is also present a considerable amount of acid insolublematter. As my method of flotation retards this material as Well as theiron oxide, the insoluble matter content of the iron product is greaterthan that of the feed. In the aforementioned copending application,Serial No. 290,842, filed.May 29, 1952, in which I am a joint inventor,there is described a process for beneficiating iron ores by frothflotation wherein a two-stage procedure of selectively beneficiatingsuch ores is employed. Complete treatment of ores containing bothcalcareous and siliceous constituents would require use of a procedureof this nature whenever the two gangue minerals were to be isolated asindividual products. I am presently concerned, however, with only thefirst stage of this. selective flotation procedure-namely, theisolation, under controlled conditions, of a major part of the calcitepresent in the ore. The following example of practice must, therefore,be evaluated only from this standpoint.

A sample of calcareous and siliceous hematite ore, locally known as BigSeam Red Ore, was obtained from the Birmingham, Alabama, district. Theore was typical of the district and contained hematite associated with agangue composed predominantly of quartz and calcite. Minor quantities ofshale and ferruginous clays also were present. A head analysis gave 36.4percent Fe, 12.0 percent CaO, and 22.4 percent hydrochloric acidinsoluble.

A 25 O-gram charge of the calcareous iron ore was ground to pass mesh inthe manner described in Example 1. The ground charge, including slime,was transferred to a small mechanical flotation cell of standard designand sufficient tap water added to give a pulp for flotation containingabout 22 percent solids. Flotation of the calcite from the slime-bearingpulp was effected by the following reagents expressed in conventionalterms ton of flotation feed:

of pounds per Conditioner Rougher Cleaner Reagent 5 No. 1 No. 2 1 No. 2

NaOH NazCOa Sodr m Silicate N 'u Red 011 Time, minutes Pulp pH Theslime-bearing pulp was conditioned with caustic, soda ash, to replacepart of the silicate, and sodium silicate N (a 40 percent aqueoussolution, added on an as received basis). Red oil was then added asfilming agent, and the pulp again conditioned briefly as indicated. Therougher froth was cleaned by refloating in the same cell, using tapwater for dilution together with additional caustic soda and silicate.The froth (calcite product) and composited Fe product (middlings plustailings) were dried, weighed, and analyzed.

The results of the test are as follows:

The flotation process resulted in the isolation of 86 percent of thecalcite with a loss of only 11.4 percent of the Fe. The composite Feproduct, though still containing siliceous material, was neverthelessincreased in grade from 36 to 44.3 percent Fe. For illustrationpurposes, subsequent treatment by the method of my copendingapplication, to reject silica, produced an over-all 85 percent Ferecovery in a final iron product having an assay of 54.7 percent Fe, 2.3percent CaO, and 12.5 percent insol.

The results of the previously described flotation tests are typical ofthose obtained on a variety of calcareous ores, using various silicatesand combinations of silicates with other iron oxide depressants asretardants while float- 0 ing calcite from iron ore pulps made alkalineto a pH above 9.3 by means of caustic soda, sodium sulfide, or by thenatural alkalinity derived from a relatively high concentration ofsilicate. Oleic acid,-or red oil, is the preferred collecting agent orcalcite promoter, in the practice of my invention, but sodium olea te,tall oil, sulfate soap, petroleum sulfonates, fish oil fatty acids, orsimilar anionic collecting agents or combinations thereof, have alsobeen successfully used for this purpose.

The practice of my invention aifords a means of positively controlling,in the case of calcareous iron ores, the quantity of calcite remainingin the ore from which a part of the insoluble matter has been, or is tobe, removed. In the event an essentially self-fluxing product is desiredfrom the beneficiation processes, positive means of assuring the properacid-base relationships are provided. The high-grade calcite isolated bymy process may readily be recombined with the iron product, oncesiliceous gangue has been removed by any of several possible methods.

The process also affords a positive rejection of the maximum quantity ofcalcite that might be desired in the event the ores or products aretransported for considerable distances to the blast furnaces.Transportation charges in some instances are sufliciently great towarrant isolation and rejection of the material at the mine and tosupply fluxing material from calcite or dolomite deposits moreimmediatelv adjacent to the furnaces.

Since many widely differing embodiments of the invention will occur toone skilled in the art, the invention is not limited to the specificdetails illustrated and described, and various changes may be madetherein without departing from the spirit and scope thereof.

What is claimed is:

1. A process for selectively isolating the calcareous constituents ofcalcareous iron ores comprising subjecting an alkaline pulp of the ironore having a pH at least as high as about 9.3 to froth flotation with ananionic-collecting agent selected from the class consisting of higherfatty acids, resin acids, mixtures of fatty and resin acids, and soapsthereof, and retarding flotation of the iron oxides with water-solublesilicates in an amount providing an iron oxide depressing actionequivalent to that of from 2 to 12 pounds of sodium silicate solution of63 per cent water content per ton of ore.

2. A process for beneficiating calcareous iron ores which comprisesconditioning an aqueous pulp of the comminuted ore with a quantity ofalkali metal silicate sufficient to establish a pulp pH at least asalkaline as pH 9.3, adding to the alkaline pulp an anion-activecollecting agent selected from the class consisting of higher fattyacids, resin acids, and mixtures of fatty and resin acids, and soapsthereof, and then subjecting said pulp to agitation and aeration wherebycalcareous diluents are floated and beneficiated iron ore is depressedand recovered.

3. A process for beneficiating calcareous iron ore comprising forming anaqueous pulp of the comminuted ore, adding alkali metal silicate and adispersing agent to the pulp in an amount providing an iron oxidedepressing action equivalent to that of from 2 to 12 pounds of sodiumsilicate solution of 63 per cent water content per ton of ore, adjustingthe pH of the pulp to at least as high as about pH 9.3, adding ananion-active collecting agent selected from the class consisting ofhigher fatty acids, resin acids, mixtures of fatty and resin acids, andsoaps thereof, to the alkaline pulp, and then subjecting said pulp toagitation and aeration, floating the calcareous material from the ironoxides and insolubles, and separately recovering beneficiated iron oxideand material high in CaO content.

4. A process for beneficiating calcareous iron ore comprising forming analkaline pulp of the comminuted ore having a pH in the range of fromabout 9.3 to about 11.0, including a quantity of alkali-metal silicatein said alkaline pulp in an amount providing an iron oxide depressingaction equivalent to that of from 2 to 12 pounds of sodium silicatesolution of 63 per cent water content per ton of ore, adding an activeanion-collecting agent selected from the class consisting of higherfatty acids, resin acids, mixtures of fatty and resin acids, and soapsthereof, to the alkaline pulp, and then subjecting said pulp toagitation and aeration, floating off the calcareous material from thedepressed iron oxides, and recovering the beneficiated iron ore.

5. A process for beneficiating calcareous iron ore comprising forming apulp of the comminuted ore, adding to the pulp a quantity of alkalinematerials including alkalimetal silicates in an amount providing an ironoxide depressing action equivalent to that of from 2 to 12 pounds ofsodium silicate solution of 63 per cent water content per ton of ore, toraise the pH of the pulp to at least about 9.3, adding an anion-activecollecting agent to the alkaline pulp, and then subjecting said pulp toagitation and aeration whereby calcareous dilutents are floated andbeneficiated iron ore is depressed, and recovering the beneficiated ironore.

6. A process for beneficiating calcareous iron ore comprising, formingan aqueous pulp of the comminuted ore, adding sodium silicate solutioncontaining about 63 percent Water to the pulp in an amount of about 8 to12 pounds of the reagent solution per ton of ore, adjusting thealkalinity of the pulp to a pH of about 10.0, conditioning the pulp forflotation by the addition of an anionic collecting agent selected fromthe class consisting of higher fatty acids, resin acids, mixtures offatty and resin acids, and soaps thereof, subjecting the conditionedpulp to agitation and aeration whereby calcareous material is floatedand beneficiated iron ore is depressed, and separately recovering thebeneficiated iron oxide and calcareous material.

References Cited in the file of this patent UNITED STATES PATENTS1,939,119 Holt Dec. 12, 1933 2,383,467 Clemmer et al. Aug. 28, 19452,403,481 Clemmer et al. July 9, 1946 2,415,416 Clemmer et al. Feb. 11,1947 2,507,012 Heilmann May 9, 1950 FOREIGN PATENTS 621,985 GreatBritain Apr. 25, 1949

1. A PROCESS FOR SELECTIVELY ISOLATING THE CALCAREOUS CONSTITUENTS OFCALCAREOUS IRON ORES COMPRISING SUBJECTING AN ALKALINE PULP OF THE IRONORE HAVING A PH AT LEAST AS HIGH AS ABOUT 9.3 TO FROTH FLOTATION WITH ANANIONIC-COLLECTING AGENT SELECTED FROM THE CLASS CONSISTING OF HIGHERFATTY ACIDS, RESIN ACIDS, MIXTURES OF FATTY AND RESIN ACIDS, AND SOAPSTHEREOF, AND RETARDING FLOTATION OF THE IRON OXIDES WITH WATER-SOLUBLESILICATES IN AN AMOUNT PROVIDING AN IRON OXIDE DEPRESSING ACTIONEQUIVALENT TO THAT OF FROM 2 TO 12 POUNDS OF SODIUM SILICATE SOLUTION OF63 PER CENT WATER CONTENT PER TON OF ORE.